What is the cause of respiratory alkalosis and tachycardia in a patient with a pontine (pontine, referring to the pons in the brainstem) stroke?

From the Guidelines

Respiratory alkalosis and tachycardia in pontine stroke patients should be managed with standard stroke protocols, including thrombolysis if appropriate, blood pressure management, and supportive care, with a focus on addressing the underlying autonomic disturbances and preventing further complications, as suggested by the most recent guidelines 1. When a stroke affects the pons, it can damage respiratory centers that regulate breathing patterns, leading to hyperventilation and subsequent respiratory alkalosis as excess carbon dioxide is blown off. This hyperventilation often manifests as Cheyne-Stokes respiration, characterized by periods of deep, rapid breathing alternating with periods of shallow breathing or apnea. Simultaneously, damage to cardiovascular regulatory centers in the pons can result in tachycardia due to disruption of parasympathetic outflow from the vagus nerve.

Key Considerations

• Management typically involves addressing the underlying stroke with standard stroke protocols including thrombolysis if appropriate within the time window, blood pressure management, and supportive care.
• For severe respiratory alkalosis, controlled oxygen therapy may be necessary, as maintaining adequate tissue oxygenation is important in the setting of acute cerebral ischemia 1.
• Persistent tachycardia might require beta-blockers such as metoprolol 25-50mg twice daily, titrated to heart rate response, with close monitoring of vital signs, arterial blood gases, and neurological status.
• The presence of these symptoms together should prompt immediate neurological evaluation as they may signal brainstem involvement requiring more aggressive intervention, with a focus on preventing cardiac complications, which account for 2% to 6% of mortality within the first 3 months 1.

Monitoring and Prevention

• Continuous ECG and cardiac monitoring for at least the first 24 hours are needed to screen for serious cardiac arrhythmias, which can occur among patients with acute ischemic stroke 1.
• A clinical cardiovascular examination, cardiac enzyme tests, and a 12-lead ECG should be performed in all stroke patients to detect cardiac abnormalities, which are prevalent among patients with stroke 1.
• Chest radiography and examination of the cerebrospinal fluid may be indicated in certain cases, but their routine use is not recommended, as they have modest value in altering clinical management 1.

From the Research

Respiratory Alkalosis and Tachycardia in Pontine Stroke

• Respiratory alkalosis is a rare but severe complication of acute ischemic stroke (AIS), resulting from hyperventilation due to the effect of stroke on the respiratory center 2.
• The condition can lead to multiple metabolic abnormalities, including changes in potassium, phosphate, and calcium, as well as the development of a mild lactic acidosis 3.
• Tachycardia is a common cardiac effect of respiratory alkalosis, which can also cause ventricular and atrial arrhythmias, and ischemic and nonischemic chest pain 3.
• In the context of pontine stroke, respiratory alkalosis can be particularly problematic, as it may lead to further complications such as hypokalemia, which can induce bidirectional ventricular tachycardia 4.
• The management of respiratory alkalosis in patients with acute ischemic stroke, including those with pontine involvement, typically involves mechanical ventilation to correct the underlying etiology 2, 5.
• The optimal mechanical ventilator strategy for these patients remains unclear, but a protective ventilatory strategy may have a role in reducing pulmonary complications 5.

Pathophysiology and Clinical Presentation

• Respiratory alkalosis occurs when alveolar ventilation exceeds that required to eliminate the carbon dioxide produced by tissues, leading to decreases in Paco2, increases in pH, and compensatory decreases in blood HCO3- levels 6.
• The condition can be acute or chronic, with metabolic compensation initially consisting of cellular uptake of HCO3- and buffering by intracellular phosphates and proteins 6.
• In patients with pontine stroke, the clinical presentation of respiratory alkalosis may be complex, involving multiple organ systems and requiring careful management to prevent further complications 3, 5.